This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Auditory hair cells are the sensory cells that transduce acoustical signals into neural ones in vertebrates, thus providing the ability to hear. In mammals, when these terminally-differentiated cells are damaged or lost, the result is permanent loss of hearing since lost mammalian hair cells do not regenerate. In fish and birds, damaged auditory sensory epithelia have the capability of regenerating new hair cells, resulting in recovery of hearing. Recent studies show that goldfish exhibit both structural (hair cells) and functional (hearing) recovery following noise exposure. To fully understand what normal cellular processes lead to regeneration in fishes, knowledge of how specific genes mediate hair cell growth (proliferation and transdifferentiation) and apoptosis is essential.